problem with sed for inserting command

Shell Programming and Scripting
1

Hello,
i use sed '/good/ a\INSERT' 1.txt command for insert a text on my file on linux butit does not work see the output :

[root@server t]# sed '/good/ a\INSERT' 1.txt
if_test=iso
ifup=eth0
Hello
World
Bye
now
good
INSERT
[root@server t]# cat 1.txt
if_test=iso
ifup=eth0
Hello
World
Bye
now
good
[root@server t]#

with sed '/good/ a\INSERT' 1.txt it will insert but when i want editing it it does not include "INSERT" would you help me what is wrong withit?

Thank You,

2

use -i option with sed command.

$ sed -i  '/good/ a\INSERT' 1.txt